Fiber reinforced resin composite structures are used in various industries, including the manufacture of parts and finished goods in automotive, recreation vehicle, trucking, aerospace, marine, rail, appliance, athletic equipment, container, construction, anti-corrosion, electrical and medical industries. There are several generally known technical approaches to the forming of fiber reinforced laminate composites.
Closed molding has existed for many years but is gaining wider adoption as manufacturers seek to reliably produce high-volume, high quality parts, yet simultaneously reduce emissions of hazardous air pollutants. In closed mold processing, fiber and/or other reinforcement(s), collectively referred to as the “pre-form,” are cut to fit and then placed in the two-part mold. A method of enclosing and compressing the pre-form against the mold is then employed. The resin is then typically introduced into the pre-form via ports through the enclosure. Upon curing of the resin, the mold enclosure member is first removed, followed by the finished part.
Of the available closed mold processes, vacuum infusion is perhaps-the easiest to use and provides engineers with an arsenal of design options to attain many benefits over other processing methods (e.g. lamination, also known as open molding) including: improved performance-to-weight, higher fiber volume ratios and efficient structural designs; reduced cost through fewer parts and production steps, efficiency of material and labor use, and simplification and standardization manufacturing methods; improved structural properties and longevity, reduced fatigue properties in structural laminate, smoother ply drop transitions and processes that increase reliability of fiber placement, orientation, and laminate composition.
There are two basic vacuum infusion techniques, surface infusion and interlaminar infusion. In surface infusion, before applying the flexible bag or membrane a disposable barrier layer, commonly referred to as a peel ply, is placed on top of the laminae pre-form. A disposable infusion medium with rigid open structures that do not buckle under vacuum and/or perforated injection tubing is then placed on top of the peel ply to aid in the delivery and distribution of the liquid resin down through the laminae stack. In the case of a reusable vacuum bag or membrane the distribution channels may be incorporated into the bag. Vacuum pressure is then applied to draw resin through feed-lines into the mold and through the fiber pre-form. This technique is commonly referred to as surface vacuum infusion processing since the resin is introduced at the top surface of the laminae assembly. Examples are described in Seemann et. al. U.S. Pat. Nos. 4,902,215, 5,052,906 and 5,601,852. The greatest drawback of surface infusion is the high waste and non-profit stream costs due to the disposal of peel plies and surface infusion medium. Other drawbacks include steep implementation learning curves and increased complexity with increases in part size. Further drawbacks will be recognized by those fluent in the art.
In interlaminar infusion the infusion medium is integrated with other laminae in the ply stacking sequence of the laminae pre-form. There are numerous advantages to interlaminar infusion processing over surface infusion processing other than waste and cost reduction. Surface infusion is a one-sided process in which the resin flows from the top down through the laminae stack. Interlaminar infusion medium can be sandwiched and/or placed on either face to promote infusion on all sides of the dry laminae, greatly speeding infusion. Further, since the composite becomes the infusion pathway, placement of vacuum and resin feed lines is greatly simplified. Those fluent in the art will recognize the maintenance of medium porosity under vacuum induced compression as prerequisite to flow efficacy.